From the U.S. Pat. No. 3,002,804, it is known to draw a synthetic yarn by means of a stretching bath. In the system of the patent, the yarn is guided through a stretching bath of relatively large volume. The bath is open at its upper end and provided at its lower end with an outlet opening for the yarn. As seen in cross section, the stretching bath is substantially larger than the cross section of the yarn bundle as seen in the running direction of yarn. There is sufficient space to allow some of the liquid entrained by and moving along at high speed with the yarn to move laterally along the floor of the vessel as the yarn exits. The liquid adhering to the yarn and exiting with the yarn at the lower part of the vessel is separated therefrom by means of centrifugal force upon deflection of the yarn.
A disadvantage of this prior apparatus is that the resistance of the yarn in the bath has to be altered by varying the level of the liquid or the viscosity or specific gravity of the liquid.
In order to overcome this disadvantage, the owner of the present invention has proposed in U.S. Pat. No. 5,046,225, an apparatus in which the yarn is pulled through a relatively narrow duct. In a commonly owned European patent application No. 04 68 918 A1, a further development is disclosed wherein, with the help of a plate located between the path of the yarn and the casing wall, a circulatory flow is enabled which flows in the zone of the yarn in the direction of movement of the yarn, and which flows in the opposite direction between the said plate and the chamber wall.
In a further development of this idea, there are two spaced apart plates between which the yarn path extends. Within the chamber the yarn and the liquid sucked along with the yarn are guided between the plates, and a counterflow arises between each plate and the respective chamber wall so that a liquid circulation arises. In this system there is a possibility of varying the distance between the two plates in order to change the friction between the yarn and the liquid.
The variable braking effect between the plates will only arise when there is a relatively small distance between the two plates of one millimeter, for example. However, it has been observed (e.g., with the help of a window) that the yarns assumed a serpentine course because deflections transverse to the direction of the run of the yarn occurred, particularly at the exit.
An object of the present invention to eliminate such deflections and to achieve a yarn course which extends in a stretched form through the stretching bath. In accordance with the invention, at least one of the opposed walls between which the yarn passes during stretching is provided with a structured surface facing the yarn to suppress vibrations of the yarn. One or both of the plates on opposite sides of the yarn path may be penetrated by holes which open up into the zone where the yarn is being drawn. An advantage of the invention is that, on the one hand, the yarn is carried in stretched form and, on the other hand, the braking effect on the yarn in the stretching bath can be varied.